Touch screens are present in many different types of common modern electronic devices, such as cellular telephones, tablet computers, portable music and video devices, personal digital assistants, portable gaming devices, and so on. In these electronic devices the touch screen is part of the user interface of the device. The touch screen typically includes a display, touch sensors, and a touch controller. The touch sensors are typically some sort of transparent sensor array, such as an ultrasonic, resistive, vibration, or capacitive sensor array, that is attached to or formed as an integral part of the display. When a user touches the sensor array either with a finger or a stylus, the sensor array generates corresponding electronic sensor signals that are provided to the touch controller. From these sensor signals, the touch controller determines the type of “touch event” along with various characteristics of the touch event, and provides this information to processing circuitry in the electronic device. The processing circuitry operates in response to this information to allow a user to control the electronic device through these touches of the touch screen.
The touch controller typically captures frame data from the touch sensors and processes this frame data to determine the type of touch event that has occurred on the touch screen. This processing is typically referred to as touch frame processing and through this processing the touch controller determines the type of touch event and the location of the touch event on the touch screen. The touch controller must detect and report (to the processing circuitry) different types of touch events, such as when a user initially touches the touch screen, when the user has stopped touching the touch screen, and when a touch is moving on the touch screen, and when a moving touch has stopped moving.
The reliable detection of whether a touch is moving, or whether a moving touch as stopped moving, can be difficult. There is accordingly a need for improved circuits and methods of detecting the movement and stopping of movement of touches on a touch screen.